The present study will provide a detailed examination of the initial adjustment of the family system to the diagnosis of mental retardation for the first-born child. A longitudinal, control- group design is proposed to examine impact on the family system from an ecological perspective, with attention to a) marital structure and functioning, b) parental involvement, stress, and functioning, c) child behavior and development, and d) community support to the family. Fathers, mothers and first-born children will be included. Direct observation, interview, self-report, and formal developmental assessment data will be collected systematically in four sessions over nineteen months. Families will include 25 with a mentally retarded child (MR) and 25 comparison families (C) matched for chronological age of the child. The study is intended to identify specific interactional patterns which differentiate MR families from C families, demonstrate the manner in which such differences develop over time, identify the process and nature of impact on marital and individual well-being, and identify social supports which facilitate adaptive adjustment. Methodological advances include assessing multiple components of the family system simultaneously and over time, and systematically examining the interrelationships among measures. Results are intended to have broad implications for understanding families and facilitating their adaptation to caring for the mentally retarded child.